The Sisow payment module that I have installed in my Frozen shop throws a "Not Found" message in the case that no bank is choosen.
it also says
The requested URL was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
The code that it is generated with, is:
tep_redirect(tep_href_link('checkout_conformation.php', 'error_message=Kies uw bank!', 'SSL'));
All credits for the solution go to Rainer:
Replace checkout_conformation to checkout_confirmation some 5-6 times in the base.php file that came in the Sisow package.

Matt, it's fixed with Rainers suggestion.
The translation is correct, there is a pull down menu for the customer to select their bank, by default the action is "kies uw bank". SO when not choosing a bank and leave the default the error appeared.
It's all fixed now.

Dank je Rainer! Het is allemaal zo simpel, als je het maar ziet.... 🙂
Thanks Rainer. That did the job.
The supplied code by Sisow iDeal contains this mistake some 6 times. I will supply them the fix. All Credits to you ofcourse....

A payment module that I have installed in my Frozen shop throws a Not Found message in a certain case.
it also says
The requested URL was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
The code that it is generated with, is:
tep_redirect(tep_href_link('checkout_conformation.php', 'error_message=Kies uw bank!', 'SSL'));
Just wanted to check quickly if there is something strange about this code......

Sorry what I meant to say is I cannot change the category at all. I usually click it once, then it highlights (sort of orange) and then I edit. But it does not highlight at all.
Again, I could be my shop, since the admin is bootstrapped by the person who set it up form me, so I suspect some more changes here and there.....

@raiwa I was about to change a catagorie image in my Frozen shop, but was unable to edit the sub-cat. I was due to this change. I changed back, all worked well. Did this a few times and it's confirmed solid. So I'll have to be more patient when loading the Categories.... 😞 It was worth the try.

For my shop it's around 5-6 seconds. It got worse after I had moved a number of categories to reduce the number of main-categories.
Maybe this helps - I would like to see it a little faster as well, but I can still live with it. if 20-30 seconds it needs attention indeed.
edit: my shop has some 1000 categories.

I am not a supporter of Brexit, but I would consider this lucky for the British.
We are getting mad in Europe, looking at this example. For those 100 people we have to change our software? NEVER as far as I am concerned.